1. Field of the Invention
The present invention relates to a wire structure of a display device and, more particularly, to a wire structure of a display device suitable for effectively isolating an upper wire through a laser cutting while preventing a damage to a lower wire in case that short occurs at the upper wires which are to be isolatedly patterned in a display device where more than 2 wires are stacked.
2. Discussion of the Related Art
In general, a liquid crystal display device is a display device that a data signal is individually supplied to liquid crystal cells arranged in a matrix form and light transmittance of the liquid crystal cells is controlled to display an image corresponding to the data signal.
Thus, the liquid crystal display device includes liquid crystal panel on which the liquid crystal cells in a pixel unit are arranged in a matrix form; and a driver integrated circuit (IC) for driving the liquid crystal cells.
At this time, in the liquid crystal panel, a common electrode is formed at one inner side of facing upper and lower substrates and a pixel electrode is formed at the other side of facing upper and lower substrate, which are then arranged to face each other. An electric field is applied to a liquid crystal layer formed between the upper and lower substrates through the common electrode and the pixel electrode. The pixel electrode is formed at each liquid crystal cell on the lower substrate while the common electrode is integrally formed at the entire surface of the upper substrate.
On the lower substrate of the liquid crystal panel, a plurality of data lines for transmitting a data signal supplied from a data driver integrated circuit to the liquid crystal cells and a plurality of gate lines for transmitting a scan signal supplied from a gate driver integrated circuit to the liquid crystal cells are formed in an intersecting direction. Liquid crystal cells are defined at every intersection of the data liens and the gate lines.
The gate driver integrated circuit sequentially supplies a scan signal to the plurality of gate lines so that the liquid crystal cells arranged in a matrix form can be sequentially selected one line by one line, and a data signal is supplied to the selected one line of liquid crystal cells from the data driver integrated circuit.
A thin film transistor used as a switching device is formed at each liquid crystal cell. As the scan signal is supplied to the gate electrode of the thin film transistor through the gate lines to the liquid crystal cells, a conductive channel is formed between the source electrode and the drain electrode of the thin film transistor. At this time, as the data signal supplied to the source electrode of the thin film transistor through the data lines is supplied to the pixel electrode by way of the drain electrode of the thin film transistor, a light transmittance of the corresponding liquid crystal cell is controlled.
FIG. 1 is a plan view of a general liquid crystal cell of a liquid crystal display device.
As shown in FIG. 1, a liquid crystal cell formed at the intersection of a data line 2 and a gate line 4 includes a thin film transistor (TFT) and a pixel electrode 14 connected to a drain electrode 12 of the thin film transistor (TFT). A source electrode 8 of the TFT is connected to the data line 2 and a gate electrode 10 is connected to the gate line 4.
The drain electrode 12 of the TFT is connected to the pixel electrode 14 through a drain contact hole 16, and the TFT includes an active layer (not shown) for forming a conductive channel between the source electrode 8 and the drain electrode 12 by the scan signal supplied to the gate electrode 10 through the gate line 4.
As the TFT forms a conductive channel between the source electrode 8 and the drain electrode 12 in response to the scan signal supplied from the gate line 4, the data signal supplied to the source electrode 8 through the data line 2 is transmitted to the drain electrode 12.
Meanwhile, the pixel electrode 14 connected to the drain electrode 12 through the drain contact hole 16 is formed wide at the region where liquid crystal is positioned at every liquid crystal cell, and made of a transparent ITO (indium tin oxide) with a high light transmittance.
The pixel electrode 14 generates an electric field to the liquid crystal layer together with the common transparent electrode (not shown) formed at the upper substrate by the data signal supplied from the drain electrode 12.
When the electric field is applied to the liquid crystal layer, liquid crystal is rotated by dielectric anisotropy and transmits light emitted from a backlight toward the upper substrate through the pixel electrode 14. The amount of transmitted light is controlled by a voltage value of the data signal.
Meanwhile, a storage electrode 20 connected to the pixel electrode 14 through a storage contact hole 22 is deposited on the gate line 4 to form a storage capacitor 18, and a gate insulation film (not shown) deposited during a process of forming the TFT is inserted between the storage electrode 20 and the gate line 4, so as to be isolated.
The storage capacitor 18 charges a voltage value of a scan signal during an interval that the scan signal is applied to the gate line 4 of the previous stage, and discharges the charged voltage during an interval that a scan signal is applied to a gate line 4 of the next stage and a voltage value of the data signal is supplied to the pixel electrode 14. In this manner, the storage capacitor 18 serves to minimize a voltage variation.
In the general liquid crystal display device, the pixel electrode 14 is formed isolated from the data line 2 formed isolatedly in a vertical direction in a pixel region, and if the mutually adjacent pixel electrodes are short, laser cutting is performed on the region where the data line 2 and the pixel electrode 14 are isolated to electrically isolate the pixel electrode 14.
FIG. 2 is a sectional view taken along line I-I′ of FIG. 2.
A fabrication process of a general liquid crystal display device using 5 masks will now be described with reference to FIG. 2.
First, a metal material (Mo, Al or Cr, etc.) is deposited by sputtering on the lower substrate 1 and patterned through a first mask to form a gate electrode 10.
Next, an insulation material such as SiNx or the like is entirely deposited on the lower surface 1 with the gate electrode 10 formed thereon to form a gate insulation film 30.
And then, a semiconductor layer 32 made of amorphous silicon and ah ohmic contact layer 34 made of n+ amorphous silicon doped with high density phosphorus (P) are successively deposited on the gate insulation film 30 and patterned through a second mask to form an active layer 36 of the TFT.
Thereafter, a metal material is deposited on the gate insulation film 30 and the ohmic contact layer 34 and patterned through a third mask to form a source electrode 8 and a drain electrode 12 of the TFT. At this time, the ohmic contact layer 34 exposed between the source electrode 8 and the drain electrode 12 is removed during a patterning process.
A passivation layer 38 made of an SiNx material is entirely deposited through a chemical vapor deposition on the gate insulation film 30 with the source electrode 8 and the drain electrode formed thereon including the exposed semiconductor layer 32.
A portion of the passivation layer 38 on the drain electrode 12 is etched through a fourth mask to form a drain contact hole 16 exposing a portion of the drain electrode 12.
A transparent electrode material is deposited by sputtering on the passivation layer 38 and patterned through a fifth mask to form the pixel electrode 14. The pixel electrode 14 is formed to be connected to the drain electrode 12 through the drain contact hole 16.
FIG. 3 is a sectional view taken along line II-II′ of FIG. 1.
An overlap relation between the data line 2 and the pixel electrode 14 will now be described with reference to FIG. 3.
First, in the process of forming the source electrode 8 and the drain electrode 12 of the TFT by patterning through the third mask, the data line 2 connected to the source electrode 8 is patterned to be regularly isolated.
And then, in the process that the passivation layer 38 made of an SiNx material is formed at the entire upper surface of the lower substrate 1 including the data line 2 and patterned through the fifth mask to form the pixel electrode 14, the pixel electrode 14 is patterned at the upper surface of the passivation layer 38 of the region where the data lines 2 are mutually isolated.
In the general liquid crystal display device, if the data line 2 and the pixel electrode 14 is extended to be overlapped by the passivation layer 38 in order to improve an aperture ratio, the inorganic substance such as SiNx or the like, a comparatively thin film as a passivation layer 38, is applied thereto, which causes a problem that signal characteristics are degraded due to parasitic capacitance of the data line and the pixel electrode 14.
Therefore, recently, an organic substance such as BCB (benzocyclobutene), SOG (spin on glass) or acryl or the like is applied as the passivation layer in fabricating a liquid crystal display device with an improved aperture ratio as well as preventing degradation of signal characteristics, since even if the data line 2 and the pixel electrode 14 are overlapped by the passivation layer, their parasitic capacitance is infinitesimal.
The liquid crystal display device with high aperture ratio will now be described in detail with reference to the accompanying drawings.
FIG. 4 is a plan view of liquid crystal cell of the general liquid crystal display device with a high aperture ratio.
As shown in FIG. 4, the liquid crystal is shown the same as that of FIG. 1 except that the pixel electrode 14 is formed overlapped with a partial marginal portion of the data line 2
The reason how the pixel electrode 14 can be formed overlapped with a portion of the marginal portion of the data line 2 is that the organic substance such as BCB, SOG or acryl or the like is formed at a thick film and applied as a passivation layer so that the parasitic capacitance of the data line 2 and the pixel electrode 14 can be minimized and thus degradation of signal characteristics can be prevented.
FIG. 5 is a sectional view taken along line III-III′ of FIG. 4.
As shown in FIG. 5, the data lines 2 are patterned isolatedly and regularly at the upper surface of the lower substrate 1, and a thick passivation film 48 made of an organic substrate such as BCB, SOG or acryl or the like with a low dielectric constant is formed at the entire upper surface of the lower substrate 1 including the data line 2. And then, the pixel electrode is formed to be overlapped with a marginal portion of the data line 2 at the upper portion of the passivation layer 48 where the data lines 2 are mutually isolated.
Therefore, in such a liquid crystal display device with a high aperture ratio, if the mutually adjacent pixel electrodes 14 are short due to a residual according to patterning of conductive films, the laser cutting should be performed on the data line 2 to isolate the pixel electrodes 14.
In this respect, however, if the laser cutting is performed on the data line 2, not only does the data line 2, the lower wire, be damaged but also the data lines 2 are short. Thus, if such the short occurs at the pixel electrode 14, its product should be discarded, causing problems that the cost of materials is increased and yield is degraded, and thus, a unit cost of the product is increased.